OnCo has just opened for review, so the roster is empty and the first name on it could be yours. Every review badge names a person, a date and a conflict-of-interest statement; this page lists everyone who has signed off a page, with a level by count. Below: the pages where a reviewer's hour counts most right now, and how to join.
Levels are editorial labels by number of signed-off pages, not credentials. Roles and affiliations are as stated by the reviewer and verified by a maintainer through the profile URL. A review is a statement about a page on a date, not an endorsement of any product.
The top of the review queue: pages ranked by how many others link to them, what is at stake if they are wrong, and how long since they were last checked. Pick one you know, read it against its sources, and sign it off.
Pick a page from the review queue, read it against its sources, and open the review issue form. You will be asked for your name, role, a profile URL for verification, what you checked, what you found, and a conflict-of-interest statement covering the last three years. A maintainer verifies identity and records the review; the badge appears on the page and your name appears here. Reviews without a COI statement are not recorded.
Have a person record in OnCo? Say so in the form and the badge links to it.